Part of the reduction comes from the direct correlation between speed and fuel consumption, but the real impact would come from behavioural changes; people would tend to shift to other, faster modes of travel, and will probably tend to move closer to where they work.

Wired questions their logic, particularly as it applies to America.Short- and long-term CO2 emission cuts as a share of total motorway CO2 emissions by cars in various scenarios

The findings assume two things. First, there is a viable alternative to driving, such as a comprehensive rail system. And second, that people want to return to urban centers. The researchers concede these points when they note the findings apply only to the Netherlands and may vary elsewhere.

Really? Isn't that what we have all been calling for, an investment in public transport, a return to walkable, denser cities? Why is there this automatic assumption that the way we have been doing things in North America is the only way it works and the way it is going to continue, with the private automobile-based low-density suburban America that we have now?

There are LOTS of reasons to lower the speed limit; we reprise them here.Six Reasons to Slow DownIt could save a lot of fuel. Some estimates indicate up to 5%; In 1983, by which time many people were ignoring it, it saved 2.5 billion gallons of gasoline and diesel, or 2.2% of the total fuel used. Oil was a horrible $ 20 per barrel. Wired notes that "The Department of Energy noted in 2008 that lowering the national speed limit to 55 mph would save 175,000 to 275,000 barrels of oil daily."

It could save a lot of lives. Speed kills. A study examined the impact of higher travel speeds on US rural interstates after the repeal in November 1995 of the national speed limit. Researchers found states that had increased their speed limits to 75 mph (120 km/h) experienced a shocking 38 per cent increase in deaths per million vehicle miles than expected, compared to deaths in those states that did not change their speed limits. States that increased speed limits to 70 mph (112 km/h) showed a 35 per cent increase in fatalities. (Canada Safety Council)It will reduce the cost of cars and could save Detroit With a lower speed limit one certainly doesn't have much need for a big honking hemi, and probably you don't need so many airbags and so much crash protection. Cars could be lighter and cheaper, take up less space, and Detroit could quit worrying about CAFE standards.

It could solve our infrastructure problems and save on taxes. As we noted in an earlier post, "Transportation officials know many of the nation's 600,000 bridges are in need of repair or replacement. About one in eight has been deemed "structurally deficient." Lighter vehicles travelling at slower speeds do far less damage to our roads and bridges. Design loads and lane widths could be adapted to the smaller vehicles. Three lane highways might become four lane; more capacity for the price of a can of paint.

It would spur innovation and investment in alternative transport if trains go four times as fast as cars, there is a lot more incentive to use them.

It would promote innovation in urban design and densification of the existing suburbs Parking lots could be scaled down, buildings built more closely together, America could begin to look more like Europe. Although most commuters probably don't move at 55 mph now, it is still likely that people might tend to want to live closer to work with a lower speed limit.